This invention relates to a method for printing, and more particularly, to a method for printing an increased number of colors utilizing a color printer having a predetermined number of colors.
There currently exists various techniques for printing in a variety of colors from a predetermined set of colors. A color ink jet printer contains liquid ink of some predetermined colors, allowing the color ink jet printer to print in this predetermined set of colors. The color ink jet printer can print additional colors, i.e. expands the predetermined set of colors, by spraying a point (pixel) on the paper with a predetermined combination of the set of colored ink such that the colors achieve a blending effect resulting in a new color, i.e. a color in addition to the predetermined set of colors. There also exists color thermal printers which are high resolution printers, having both an external resolution and an internal resolution, and allow color mixing as the ink jet printers. The external resolution allows a pixel to be addressed by attached external equipment (i.e., a processor or computer system). When the processor desires to use the printer, the processor sends command information to the printer to print a specified pixel in either a "pure" color or a "non-pure" color (non-pure is used here in the sense that the thermal printer has a predetermined set of solid ink cartridges which allows printing in the set of "pure" colors, and "non-pure" is a predetermined combination of the "pure" colors). The pixel of the color thermal printer has an internal resolution (i.e., high resolution) which is utilized by the printer. Thus, if the thermal printer has a 2 by 2 internal resolution, there are four "sub-pixels" which are not addressable by the external equipment. If the color thermal printer is commanded to print a non-pure color, the internal logic of the printer causes each of the 4 "sub-pixels" to be printed with a predetermined pure color such that the blending effect of the human eye will be observed as the commanded non-pure color. In this manner, high resolution color printers achieve an expansion of the color set of the high resolution printer.
The present invention provides a method which results in expanding the set of colors which can be printed on a low resolution printer.